Secondary ion emission SIMS - Principles and equipment

Secondary Emission Ion Analysis (SIMS) is one of the materials analysis methods based on ion bombardment. It can be described as a microanalysis method, in the sense that the volume instantaneously analyzed is much smaller than a micrometer. It is based on irradiation by heavy ions (or neutral monoatomic particles) of medium and low energy (1 to 50 keV). The interaction of the incident beam with the material results in a cascade of collisions, leading both to the implantation of primary particles and to the sputtering of the target in the form of charged (secondary ions) or uncharged particles. It is these charged particles (ionized during the sputtering process, or sometimes obtained by post-ionization of neutral sputtered particles) that are filtered by mass (and possibly by energy) to access the composition of the target sample.

The general performance of secondary emission ion analysis of solid materials can be summarized as follows:

• very high sensitivity (very low detection limits) for almost all elements of the periodic table (trace analysis);

• access to elemental isotope analysis (use of isotopic tracers);

• dynamic determination of concentration profiles from the surface to very shallow depths (analysis of thin films or diffusion profiles);

• the possibility, in the static regime, of accessing the composition, possibly molecular, of the first atomic or molecular layers;

• spatial location of elements, or in some cases chemical species, with good lateral and depth resolution;

• the use of "matrix" chemical effects to identify, and possibly quantify, chemical compounds.

The complexity of the mass spectra obtained, and the difficulties involved in quantifying them, mean that this method is not suited to the identification and quantitative analysis of alloying elements in high concentrations in solid materials, for which less expensive and faster methods such as electron microprobe, analytical scanning microscopy, chemical analysis, etc. are more appropriate.

We begin by summarizing a few principles of secondary ion emission phenomena, a knowledge of which is essential for the correct interpretation of analyses. A simplified description of the equipment used will then explain how data are obtained, so that the most important experimental parameters in materials analysis can be rationally identified. The wide range of analytical procedures made possible by this method will be reviewed in P 2 619, with the aim of guiding the reader in choosing the analytical conditions that will deliver the best performance in the areas...